Electronic timer circuits providing switching at multiple intervals



July 22, 1969 K. D. wALLEN'rowlTz 3,457,464

ELECTRONIC TIMER CIRCUITS PROVIDING SWI'ICUNG AT MULTIPLE INTERVALSFiled Feb. 15. 1967 l/UYACA 51 smnr Na'krn Ware 8a Daw/s Hrrokmsys.

United States Patent O 3,457,464 ELECTRONIC TIMER CIRCUITS PROVIDINGSWITCHIN G AT MULTIPLE INTERVALS Klaus D. Wallentowitz, Waterbury,Conn., assignor to General Time Corporation, Stamford, Conn., acorporation of Delaware Filed Feb. 15, 1967, Ser. No. 616,370 Int. Cl.Htllh 47/18 U.S. Cl. 317-142 5 VClaims ABSTRACT F THE DISCLOSUREenergization of the second relay, connect the lter capacitor into acircuit providing a predetermined discharge time. The rst relay isconnected across the lter capacitor and thus drops out a predeterminedsecond time interval subsequent to the energization of the second relay.

The first timed interval is detected by a unijunction transistor. Theenergization of the second relay is controlled by a silicon controlledrectifier. A resistor is connected across the second relay coil toprovide an initial current path for initially turning on lthe siliconcontrolled rectifier. A capacitor is connected across the bases of theunijunction transistor to stabilize the base 1 to base 2 voltage of theunijunction transistor against transients. A resistor is connectedbetween the output of the unijunction transistor and the gate of the SCRwhich in combination with another resistor connected in circuit with thegate and cathode of the SCR lengthens the pulse provided by theunijunction transistor so that the relay SCR circuit may be operatedfrom half-wave rectified alternating current.

Related applications The timer disclosed in the present applicationutilizes the bridge circuit timer invention disclosed and claimed in myco-pending application, Ser. No. 405,503, tiled Oct. 21, 1964, entitledElectronic Timer Circuit (now Patent No. 3,355,632 issued Nov. 28,1967). That application is assigned to the same assignee as the presentinvention and is incorporated herein by reference.

The present invention was made during a program of electronic timerdevelopment at applicants assignees Industrial Controls DivisionEngineering Department and the following United States patentapplications resulting from said development exemplify the prior art:The United States patent applications of Robert S. Lundin, Ser. No.472,844, filed July 19, 1965, entitled Condition Responsive InputControllers; Ser. No. 479,553, filed Aug. 13, 1965, entitled ConditionResponsive Process Timer; 4(now Patent No. 3,393,604 issued July 23,1968) Ser. No. 589,335, -filed Oct. 25, 1966, entitled Relay Circuit forHalf-Wave Alternating Current Energization and Electronic TimerEmploying the Same, Ser. No. 590,- 707, filed Oct. 31, 1966, entitledElectronic Timer Circuits; my United States patent applications, Ser.No.

589,336, filed Oct. 25, 1966 (now Patent No. 3,417,296 issued Dec. 17,1968); Ser. No. 591,016, filed Oct. 31, 1966 (now Patent No. 3,417,297issued Dec. 17, 1968); Ser. No. 615,527, all entitled Electronic TimerCircuit(s); the United States patent application of George I. Yagusic,entitled .Delay on De-energzation Electrical Timers, Ser No. 595,993,filed Nov 21, 1966; and the United States patent applications of EdwardT. Bosman entitled Electronic Timer Circuits, Ser. No. 595,955, filedNov. 21, 1966, and Ser. No. 601,780, filed Dec. 14, 1966s All of theabove-identified applications are assigned to the same assignee as thepresent application and are incorporated herein by reference.

Background of the invention This invention relates to electronic timercircuits providing switching at multiple intervals. More particularly,it relates to such an electronic timer for connection to a Source ofalternating current wherein a single capacitor performs the dualfunctions of acting as the filter, capacitor in the rectifying networkfor supplying direct current to a first interval timing network; and,upon completion of the first timing interval, of providing the time basefor a second timing interval. To this end, transfer contacts on a relayoperated at the end of the first timing interval alternately connect thedual function capacitor into appropriate circuits.

Such timers are employed in original manufacturers equipment and areutilized to provide successively timed load circuit controllingswitching functions.

It would be obvious, according to the prior art, to provide a timedsuccession of relay contact transfers by connecting a second interval ordelay timer energized upon the conclusion of the timing operation of afirst interval or delay timer. Such a circuit would be relativelyexpensive; however, in that two time interval bases, such as theresistance-capacitor bridge charging circuits disclosed in myabove-identified application, Ser. No. 405,503, would have to beprovided along with separate detection circuits therefor and separateload relay controlling circuits. Thus, such timers, according to theprior art, might include a pair of timing capacitors, a pair of detectorsemiconductor devices, and a pair of silicon controlled rectifiers orother load controlling switching devices.

It is known, according to the above-identified applications, to operatea relay from half-wave rectified alternating current by connecting adiode in parallel across the energization coil of the relay. Forexample, such a circuit is disclosed and claimed in the above-identifiedapplication of Robert S. Lundin, Ser. No. 589,335, wherein theenergization of the relay is under control of a silicon controlledrectifier (SCR). One diiculty I have discovered with this circuit isthat the relay may not always energize during the first positive half ofthe AC cycle subsequent to the timed interval because transientsdeveloped when initially energizing the relay coil may prevent enoughcurrent from being supplied to the cathode of the SCR to switch it toits conducting state.

In my above-identified application, Ser. No. 589,336, I disclose andclaim a circuit utilizing a unijunction transistor for detecting thecompletion of a timing interval measured in a RC timing circuit. Theload relay is controlled by a silicon controlled rectifier and in orderto provide transient protection therefor, I connect a resistor and acapacitor in parallel across the gate and cathode terminals of the SCR.I also provide a diode connected between the base 1 of the unijunctiontransistor and the gate terminal of the SCR. As described in thatapplication, this circuit stretches out the short pulse supplied by theunijunction transistor at the completion of the timing 1nterval so thatit is longer than one-half of the altern-atlng current cycle time inorder to insure that the SCR turns on, since it is operated frompulsating half-wave alternating current. I have discovered that thisaction may be greatly improved at less expense by substituting aresistor for the diode connected between the base of the uni]unc tiontransistor and the gate of the SCR.

I have further discovered that the unijunction transistor is verysensitive to transients, especially near the end of the timing intervalwhen the timing capacitor is nearly fully charged; and that thissensitivity can be greatly reduced by connecting a capacitor in circuitacross the bases of the unijunction transistor.

Summary of the invention It is, therefore, an object of the presentinvention to provide an electronic timer circuit providing switching atImultiple intervals.

A further object of the invention is to provide a timer circuit of theabove character in which said switching functions are provided byindependent relays.

Still another object of the invention is to provide a timer circuit ofthe above character in which the timing determining elements arecapacitors.

A further object of the invention is to provide a timer circuti of theabove character in which the switching functions `are controlled bysemiconductor devices.

A still further object of the invention is to provide a timer circuit ofthe above character utilizing a unijunction transistor as a timingdetector device.

A yet further object of the invention is to provide a timer circuit ofthe above character utilizing a load circult comprising a siliconcontrolled rectifier controlling a relay operated from half-waverectified alternating current under control of the unijunctiontransistor.

Another object of the invention is to provide a timer circuit of theabove character providing inherently more secure initial energization ofsaid load circuit than according to the prior art.

Yet another object of the invention is to provide a timer circuit of theabove character providing inherently greater protection againsttransients for said unijunction transistor.

. Still another object of the invention is to provide an electronictimer circuit of the above character providing an advantageous pulsestretching circuit connected between the unijunction transistor and theSCR.

A further object of the invention is to provide an electronic timercircuit of the -above character utilizing a minimum number ofinexpensive components.

A still further object of the invention is to provide an electronictimer circuit of the above character of increased reliability.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the features of construction,combinations of electrical elements, and electrical circuit arrangementswhich will be exemplified in the electronic timer circuit hereindisclosed. The scope of the invention is indicated in the claims.

The present invention is exemplified in the electronic timer shown inFIGURE 1 of the drawing. Momentary contact closure initiation isprovided by depressing start switch S1. This quickly energizes relay RY1through switch S4 since capacitor C1 quickly charges. Relay RYlscontacts S2 then transfer to complete a holding circuit keeping relayRY1 energized and supplying power to the remainder of the timer circuit10. Capacitor C1 acts as a filter capacitor providing direct currentbetween busses 16 and 18. Timing capacitor C2 is charged throughvariable resistor RS. Unijunction transistor UT fires after apredetermined interval; and the pulse provided thereby is stretched byresistors R10, R11 and R8 to provide a triggering pulse to the gate ofthe silicon controlled rectiier SCR.

Relay RYZ then energizes, transferring contacts S4. Because of thecharge on capacitor C1, relay RY1 remains energized. Capacitor C1 thendischarges through variable resistor R2, resistor R3, and relay RY1.When the voltage across relay RY1 falls to its dropout level, relay RY1deenergizes, transferring contacts S2 thereof, de-energizing the timercircuit. Relay RYZ de-energizes and timing capacitor C2 dischargesthrough resistor R6 to provide a quick reset feature. The relays RY1 andRYZ are thus operated, as shown in FIGURE 2, for the intervals 26 and28, respectively.

The unijunction transistor UT is protected against transients by acapacitor C3 connected between its base 2 terminal 20 and the negativebus 18, thus forming with resistor R8 a circuit between base 1 terminal22 and base 2 of the unijunction transistor.

Resistor R13 connected across the coil of relay RYZ provides an initialpath for current to the SCR to insure that it turns on in spite of anytransients caused by the initial energization of relay RY2.

Resistor R10, connected in circuit with resistor R11, stretches thepulse supplied by the unijunction transistor UT so that it is longenough to insure that the SCR will turn on during the next succeedingpositive portion of the pulsating alternating current on load conductor24.

The drawing For a fuller understanding of the nature and objects of theinvention, reference should be had to the following detaileddescription, taken in connection with the accompanying drawing, inwhich:

FIGURE 1 is a schematic electrical circuit diagram of a preferredembodiment of my invention; and,

FIGURE 2 is a timing diagram illustrating the operation of theembodiment of FIGURE 1.

Specific description Now referring to FIGURE 2 of the drawing, thecustomer specifications for the timer 10, shown in FIGURE 1, are thatupon depressing the start switch S1, relay RY1 will be energized for 700milliseconds as shown at 26 in FIGURE 2, and that relay RYZ will beenergized for 100 milliseconds just before relay RY1 de-energizes asshown at 28 in FIGURE 2. These functions are effected as follows:

Depressing the start switch S1 connects the timer circuit 10 to a sourceof 110 vo-lt alternating current connected across terminals 12 and 14.The current passes through dropping and surge resistor R1, is rectifiedat diode D1, passes through contacts S4 and quickly charges capacitorC1. Enough current then iiows through resistor R3 and relay RY1 toenergize relay RY1. Upon energization, relay RY1 transfers its contactsS2 to furnish a holding circuit to keep the timer 10 connected incircuit with terminals 12 and 14.

In combination with resistor R4, capacitor C1 now acts as a filter sothat direct current is supplied Ibetween positive buses 16 and 18. Thiscurrent charges timing capacitor C2 at a rate determined by the settingof variable resistor R5. Unijunction transistor UT has its bases 20 and22 connected in circuit with a biasing network formed by potentiometerP3, resistor R9, and base resistors R7 and R8. When the charge oncapacitor C2 reaches a predetermined value, unijunction transistor UTfires, that is, its emitter terminal 30 becomes essentially shorted toits base 1 terminal 22, so that capacitor C2 discharges into a networkformed of resistors R8, R10, and R11. The time constant of this outputpulse is equal to the resistance provided by resistor R8 connected inparallel with-resistors R10 and R11, multiplied by the capacitance ofthe timing capacitor C2. By choosing R10 appropriately this can beconveniently made longer than the half cycle period of the linefrequency, e.g., 19 milliseconds, so that the gate 32 of the SCR willremain conditioned for turning the SCR on until the next positive halfof the A.C. cycle.

Power for the load circuit is supplied through dropping and surgeresistor R1 and is rectified by diode D2. The resulting pulsatinghalf-wave rectified alternating current is supplied on line 24 to theparallel connected relay RY2, diode D3 and resistor R13. Resistor R13insures that current will iiow to the anode of the SCR and that it willturn on during the next succeeding positive half cycle when the gate 32is conditioned by discharge of capacitor C2. Diode D3 insures that therelay RY2 remains energized during the negative half cycles, as morefully explained in the above-identified application of Robert S. Lundin,Ser. No. 589,335. Diode D4 biased by resistor R12 biases the SCR againsttransients, as explained in my above-identified applications, Ser. Nos.589,336 and 591,- 016. Capacitor C4 and resistor R11 also protect theSCR against transients and noise, as also explained in thoseapplications.

Upon energization, relay RY2 closes contacts S3 thereof to form aholding path so that the SCR does not have to be maintained in itsconducting condition. Relay RY2 will remain energized until removal ofpower by the transfer of contacts S2 of relay RY1. Upon the energizationof relay RY2, its contacts S4 transfer disconnecting capacitor C1 fromthe timing circuit and connecting it in circuit with variable resistorR2. Capacitor C1 then discharges through variable resistor R2 andresistor R3 and relay RY1, maintaining relay RY1 energized for apredetermined period of time which is adjusted by adjusting variableresistor R2. When the voltage on the relay RY1 reaches its dropoutvalue, relay RY1 de-energizes and its contacts S2 transfer, removing thetimer 10 from circuit connection to the ll() volts AC across terminals12 and 14- Relay RY2 thereupon substantially immediately drops out asillustrated in FIGURE 2. Furthermore, contacts S2 connect resistor R6across capacitor C2 to quickly discharge it, quickly resetting the timer10 `for the next possible energization through closure of start switchS1.

By providing potentiometer P3, I am able to adjust the time range of theinitial timing interval. Connecting capacitor C3, as shown in FIGURE 1,is very effective in keeping the voltage between base 1 (22) and base 2(20) of unijunction transistor UT isolated from fiuctuations in the D C.voltage between buses 16 and 18 either introduced by line transients orby high frequency radiation.

The values of components that may be used inthe timer 10 of FIGURE 1 toprovide for 700 millisecond energization of relay RY1 and 100millisecond energization of relay RY2, as shown in FIGURE 2, are asfollows:

The unijunction transistor UT may be a type TIS43, supplied by TexasInstruments; the SCR a type C106B, supplied by the General ElectricCompany; diode D1 may 'be a type DE300; diodes D2 and D3, types DE200;and diode D4, type DE50, all supplied -by Semiconductor Products.Capacitor C1 may be an 8O microfarad, 200 volt capacitor; capacitor C2 a50 microfarad, 50 volt capacitor; capacitor C3 a .001 microfarad, 20volt capacitor; and capacitor C4 a .l microfarad, 10 Volt capacitor.Resistor R1 is then a l() ohm, 1/2 watt resistor; resistor R2 takes theform of a 4.7 kilohm, 1/2 watt fixed resistor, and a 10 kilohmpotentiometer connected in series; resistor R3 is a 6 kilohm, 5 wattresistor; resistor R4, 33 kilohms, l watt; and variable resistor R5takes the form of a fixed 33 kilohm, 1/2 watt resistor connected inseries with a l() kilohm potentiometer. Resistor R6 is 22 ohms; resistorR7, l0() ohms; resistor R8, 470 ohms; resistor R9, 4.7 kilohms; resistorR10, l kilohm; resistor R11, l kilohm; resistor R12, 47 kilohms, all 1/2watt resistors; and resistor R13 is a 10 kilohm, one

watt, resistor. Potentiometer P3 is a 5 kilohm potentiom- 75 6 eter.Relay RY1 has a resistance of 2.5 kilohms and relay RY2 is a 48 volt DCrelay.

Those skilled in the art will realize that many variations are possibleaccording to my invention of using capacitor C1 as both a filtercapacitor and a second time interval determining capacitor; that thecapacitor C3 connected in circuit lwith the bases of the unijunctiontransistor UT is of general utility when utilizing a unijunctiontransistor as a detector in electronic timers; that the pulse stretchingeffect of resistor R10 is of general utility in timers utilizinghalf-wave energization of semiconductor ycontrolled rectifier controlledload circuits; that the connection of a resistor R13 across relay RY2 toinsure enough current to properly fire a SCR connected in seriestherewith is also of general utility in timers wherein a relay isenergized through a SCR.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description are efficiently attained, andsince certain changes may be made in the above circuit without departingfrom the scope of the invention, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. An electronic timer circuit providing switching at multiple intervalscomprising:

(A) a first relay (a) connected for energization at the beginning of afirst timing interval;

'(B) a second relay (a) connected for changing its state upon thecompletion of said first timing interval,

(b) contacts upon said second relay connected in circuit with theenergization terminals of said first relay and arranged to disconnectsaid first relay from its source of energization;

(C) energy storage means connected in circuit with said first relay formaintaining its energization for a predetermined interval subsequent tothe energization of second relay, said energy storage means cornprisinga capacitor connected in circuit across the energization terminals ofsaid first relay.

(D) a direct current energized timing circuit controlling said secondrelay; and

(E) a direct current supply for said timing circuit (a) said capacitorbeing connected by said contacts on said second relay during said firsttiming interval such as to act as the filter capacitor of said directcurrent supply.

2. An electronic timer circuit as defined in claim 1 and a variableresistor connected in circuit with said capacitor by said second relayat the completion of said first timing interval.

3. An electronic timer circuit providing switching at multiple intervalscomprising:

(A) a first relay (a) connected for energization at the beginning of afirst timing interval;

(B) a second relay (a) connected for changing its state uponthecompletion of said first timing interval,

(b) contacts upon said second relay connected in circuit with theenergization terminals of said first relay and arranged to disconnectsaid first relay from its source of energization;

(C) energy storage means connected in circuit with said first relay formaintaining its energization for a predetermined interval subsequent tothe energization of second relay, and

(D) contacts on said first relay for, when said first relay isenergized, connecting it and said second relay in circuit with a sourceof electrical energy.

4. An electronic timer circuit as defined in claim 3 and 7 f y s 1 (E) amomentary contact switch connected in parallel 3,286,135 11/1966 Haveret al S17-142 across the contacts of said rst relay. 3,320,440 5/ 1967Reed. 5. An electronic timer circuit as defined in claim 4 3,406,295 10/1968 Corey 307-141 XR wherein said second relay is normallyde-energized.

JOHN F. COUCH, Primary Examiner 5 Refefences Cted W. M. SHOOP, J R.,Assistant Examiner UNITED STATES PATENTS 2,497,656 2/1950 Clarke 317-139XR 'Us' Cl- X'R' 2,902,707 9/1959 Bearer 317139 XR 307-141; B17-148.5,154

